That depends on which property of the water you need to measure.
-- Its temperature . . . degrees Celsius or Fahrenheit.
-- Its volume . . . liter or fluid ounce.
-- Its weight . . . Newton or pound.
-- Its mass . . . kilogram or pound.
-- Its conductivity . . . Siemens.
-- Its depth . . . inch or centimeter.
-- Its clarity or purity . . . I don't know units for either of those, but my only point
is that you don't "measure water" . . . you measure its properties.
I am guessing you can use Gallons.
The unit of measure here would probably be l, for liters.
Which unit would you use to measure the water in a full tub?
Gallons
Litres
I am guessing you can use Gallons.
The unit of measure here would probably be l, for liters.
Liters would be easiest to use.
Liters (L) is the best metric unit to measure the amount of water in a pool as it provides a convenient measurement for large volumes of liquid.
Measure its dimensions in inches or centimeters, and its volume or capacity in gallons or litres.
Which unit would you use to measure the water in a full tub?
Gallons.
Gallons
If you are trying to measure concentration of salt in water you would be measuring molarity which is moles / liter. Moles are equal to grams of salt / the MW of salt (and if you mean NaCl then the MW is 58.44 g/mol). Density is a ratio of mass to volume (mass / volume or kg/m^3)
You would use the metric unit "liters" to measure the capacity of a hot water tank.
gallons
Litre